Typical prior art sheet feeders commonly turned on the feed wheels once for each cycle of sheet feeding to drive the sheet of paper out of the sheet tray. Once a sheet was singly fed, the sheet could be handled and processed by any number of means well known to the art. However, obtaining single sheet feed is difficult and is affected by several factors; the normal force of the drive rollers to the sheet of paper; driver roller to sheet friction, the paper weight, humidity, inner sheet friction, edge welding, rough edges, excessive curl, paper size (out of specification), etc. It would be desirable if a technique could be provided wherein only the first sheet on top of a paper stack can be selectively driven out of the paper stack.
U.S. Pat. No. 4,290,593 describes a technique for removing the top sheet from a stack of sheets. In particular, a stack of sheets is supported in a tray, the tray having corner separators for providing that only one sheet at a time will be fed from the tray. An overhead feed roller is in contact with the top sheet of the stack, the roller being supported on an arm which is spring biased towards the stack. When it is desired to feed the top sheet from the stack, the arm and roller are advanced on a first forward stroke toward the corner separators. The roller, having been in frictional contact with the top sheet, will tend to cause the top sheets to buckle thereby allowing the forward corners of the top sheet to be removed from the corner separators. The arm and roller are then advanced rearwardly until the rearmost position is reached. In its rearward travel, the roller is able to roll upon the top sheet of the stack.
When the roller reaches the rearward end point, it is again advanced forwardly to the initial rest position. With such movement, a thin sheet which had previously been advanced a short distance will be fully advanced. Thicker sheets will be conveyed by the second forward stroke of the cycle if the thicker sheet was not separated from the corner separators on the first stroke due to its greater stiffness.
While the aforementioned patent describes a system for removing a top sheet from a stack of sheets, the disclosed technique is more costly and complex than is desired. For example, a feed brake (or one-way clutch) and arm support are necessary for system operation thereby increasing system cost and decreasing system reliability. Further, two forward feeding strokes are required which necessarily reduces system throughput.